The present invention relates to improved seat rings for use in ball valves, and to valves incorporating the same, which are operative to relieve excess cavity pressure in the valve that, in the absence of the invention, could impair or destroy operation of the valve.
Problems which may arise when excessive pressure builds up within the cavity of a ball valve are in themselves well known to those skilled in the art, and various techniques have been suggested heretofore to eliminate or minimize such problems. One such approach has been the provision of a vent hole in the upstream side of the ball itself. This approach has the disadvantage, however, that the valve is unidirectional, and may have through leakage if the ball is installed incorrectly. Recognizing this, bidirectional valves capable of relieving excessive cavity pressure have been suggested wherein, typically, the seat rings on both sides of the valve are provided with strategically located grooves. Arrangements of this latter type are described for example in Priese U.S. Pat. No. 3,488,033, Wright U.S. Pat. No. 4,236,691, and published U.K. Patent Application GB 2023773A. These latter approaches give rise to still further problems, however, e.g., the grooves which are provided in the seat rings tend to impair their sealing functions and, in any event, are normally so arranged that excessive cavity pressure tends to be relieved entirely or in major part on the downstream side of the ball. As a result, the relief of excess cavity pressure may cause the valve to leak a quantity of hazardous or dangerous fluid from its downstream side into the atmosphere under conditions where, for purposes of safety, the valve should actually be sealing against such leakage.
In this latter respect, a ball valve may be so arranged in a pipeline that it "dead ends" the line, i.e., when the valve is opened, the fluid being controlled by the valve is emitted directly into the atmosphere. If the fluid being controlled is potentially hazardous, e.g., chlorine, and the relief of excessive cavity pressure is effected at the downstream side of the valve (rather than at the upstream side, back into an upstream pipeline, as in the present invention), the resulting release of fluid into the atmosphere may be dangerous to personnel in the vicinity. Moreover, if in such an arrangement the fluid is flammable and excessive cavity pressure within the valve occurs as a result of a fire, a pressure relief operation which involves a discharge of the flammable fluid past the downstream side of the valve into the atmosphere may increase the intensity of the fire.
The present invention obviates the foregoing problems by providing an improved seat ring, and a ball valve incorporating such seat rings, so arranged that the valve, although bidirectional, seals only on its downstream side and relieves excess cavity pressure only past the upstream side of the valve. This highly desirable mode of operation is achieved by use of a modified form of seat ring of the general type shown in Sanctuary U.S. Pat. No. 2,930,576, issued Mar. 29, 1960, for "Ball Valve". The modifications constitute, in effect, the addition of certain auxiliary relief passages appropriately located in the seat ring so as to cooperate, in a proper manner, with the relief passages already provided in that ring, along with a modification of the seat ring supporting structure within the valve housing itself adapted to permit proper flexing of the lip of the seat ring.